Semiconductor device including interlayer dielectric film layers and conductive film layers

ABSTRACT

A first interlayer dielectric film layer is formed on a P-type semiconductor substrate. First connection holes are formed at specified positions of the first interlayer dielectric film layer. A first conductive film layer is formed in a region including at least the first connection holes and is composed of three layers by sequentially laminating a barrier metal film, an aluminum alloy film, and an anti-reflection film. A second interlayer dielectric film layer is formed on the first conductive film layer and is composed of a lower layer of silicon oxide film, an intermediate layer of silicon oxide film made of inorganic silica or organic silica, and a upper layer of silicon oxide film. Specified positions of the second interlayer dielectric film layer are selectively removed to form second connection holes. A second conductive film layer is formed thereon and is composed of two layers of refractory metal film in the bottom layer and aluminum alloy film in the top layer.

This application is a continuation of application Ser. No. 08/465,685,filed Jun. 6, 1995, abandoned, which is a division of application Ser.No. 08/369,253, filed Jan. 5, 1995, U.S. Pat. No. 5,459,353, which is acontinuation of application Ser. No. 08/116,947, filed Sep. 7, 1993,abandoned, which is a continuation of application Ser. No. 07/834,620,filed Feb. 12, 1992, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the reliability of connection holesbetween wirings formed within a semiconductor device, and moreparticularly to a semiconductor device having a much higher reliabilitythan a conventional connection hole structure and a method offabricating the same.

2. Description of the Prior Art

Recently, as the degree of integration of semiconductor devices hasadvanced, wiring layers have tended to be produced with finer dimensionsand their number has multiplied.

At the present, leading the progress of finer dimension technology ofsemiconductor devices, semiconductor memories have been developed bymaking use of multilayer wiring technology.

Multilayer wiring technology employs a polycide film with two layers ofpolycrystalline silicon and a refractory metal silicide. It is, however,difficult to obtain multilayer wiring with aluminum alloy film whenmultiple layers and finer dimension layers are desired. Therefore, asingle layer is used for forming a wiring layer with aluminum alloyfilm.

However, the sheet resistance of a wiring layer using polycide film isabout one hundred fold higher than the sheet resistance of a wiringlayer of aluminum alloy film. Accordingly, when manufacturing asemiconductor device which operates at high speed, a wiring delay due topolycide film occurs. Thus, in comparison with a semiconductor devicecomprised of aluminum alloy film, a semiconductor device comprised ofpolycide film, capable of operating at high speed, is not obtained. Itis hence important to realize both fine dimension and multiple layersusing aluminum alloy film with a low sheet resistance, therebymaintaining the reliability of the semiconductor device using it.

In addition, along with the progress of finer dimension technology,there is a trend which relates to finer dimension technology in thefield of microcomputer devices such as logic, Application SpecificIntegrated Circuit (ASIC), and gate arrays. In particular, in the fieldrelating to microprocessing units (hereinafter called the MPU), theoperating speed and function of the MPU are upgraded progressively.Therefore, the development of finer dimension technology formicrocomputer devices is expected to be developed. CPU performancevaries with the size of the data to be handled. For example, in the same32-bit MPUs, the performance is determined by the constraints imposed asa result of the provided function and its operating frequency, that is,the maximum processing speed.

At present, the operating frequency for a 32-bit MPU is about 50 MHz.The degree of integration of a 32-bit MPU is realized by forming1,000,000 transistors in an area of 15 mm×15 mm or less. Moreover, inorder to raise the operating frequency and in order to realize highfunctionality with an MPU, an enhancement in the degree of integrationis indispensable. Accordingly, a more sophisticated finer technology isneeded.

In the field of MPUs, in order to operate at high speed as well as torealize high function, attempts have been made to avoid the lowering ofoperating speed due to wiring delay. For this purpose, hitherto,multilayer wiring using aluminum alloy film has been employed. Toimprove the performance of the MPU, therefore, it is important toincrease the dimensional fineness achievable with multilayer wiringtechnology using aluminum alloy film.

Several problems which result from increased dimensional fineness ofwiring using aluminum alloy film are deterioration and breakdown ofwiring by migration. Such reliability problems relating to semiconductordevices are major factors which impede the progress of improveddimensional fineness technology.

Migration is classified into two areas: electromigration and stressmigration. Much has been reported relating to the deteriorationphenomenon which results in wiring as a result of stress migration. Forexample, stress migration is described in the 25th Annual ProceedingsReliability Physics 1987, pp. 15-21, "The Effect of Cu Addition toAl--Si interconnects on Stress Induced Open-Circuit Failure." Stressmigration occurs when wiring, comprised of aluminum alloy film, issubjected to the stress of an interlayer dielectric film surrounding thewiring and the passivation film and the temperature history in theparticular circumstances. As a result of the stress and temperaturehistory, the aluminum atoms in the aluminum alloy film are moved. In theresulting positions of the moved aluminum atoms, cavities (called voids)are formed in the wiring. As the voids grow, the wiring is finallybroken down. This phenomenon is called stress migration. In the abovearticle, the addition of copper elements to aluminum alloy film isdescribed. As a result, copper elements precipitate into the interfaceof the crystal grains of the aluminum film, thereby suppressing movementof aluminum atoms. It has thus been reported that the resistance tostress migration has been improved. This reported case is realized bypaying attention to the wiring of the aluminum alloy film.

On the other hand, for finer dimension multilayer wiring technologyusing aluminum alloy film, as the width of wiring is reduced, it issimultaneously necessary to reduce the size of connection holes forconnecting upper and lower wirings. The diameter of the connection holesfor connecting upper and lower wirings must be smaller than the minimumwidth of the upper and lower wirings. For example, if the width of thewiring is 1.0 μm, the diameter of the connection hole must be 1.0 μm orless. If connection holes are used which have a diameter which isgreater than the minimum width of the wiring, the width of the wiring islimited by the size of the connection holes. Accordingly, the density ofthe wiring cannot be raised easily, and the degree of integration cannotbe enhanced. Hence, the chip size is larger if semiconductor deviceshaving the same functions are used.

The prior art is described below with reference to the drawings. FIG. 8is a process sectional view showing a prior art method of manufacturinga semiconductor device in the prior art. A first conductivity typesemiconductor substrate is exemplified by P-type semiconductorsubstrate 1. In the P-type semiconductor substrate 1, it is assumed inthe following explanation that the semiconductor elements of an ordinaryMOS transistor, a MOS capacitor, a bipolar transistor and resistance isformed (not shown).

On the P-type semiconductor substrate 1, a silicon oxide film forms afirst interlayer dielectric film layer 2. The silicon oxide film is forexample, SiO₂ film, BPSG (Boron-Phospho-Silicate Glass) film, or PSG(Phospho-Silicate Glass) film formed using low pressure chemical vapordeposition or atmospheric pressure chemical vapor deposition techniques.

Next, a specified position of the first interlayer dielectric film layer2 is selectively removed. A first connection hole 4 is formed in theremoved region. The P-type semiconductor substrate 1 is exposed on thebottom of the first connection hole 4. The native oxide film formed onthe exposed semiconductor substrate 1 is removed. Afterwards, a firstconductive film layer 3 is formed in the specified region including thefirst connection hole 4 (FIG. 8A). This first conductive film layer 3 isformed in a desired pattern by anisotropic etching such as Reactive ionEtching (hereinafter called RIE). Later, heat treatment is effected at atemperature of about 450° C. (FIG. 8B).

In succession, a second interlayer dielectric film layer 6 is formed onthe first conductive film layer 3.

Next, a specified position of a second interlayer insulation film layer6 is removed selectively. The removed region becomes a second connectionhole 5. A native oxide film is formed on the first conductive film layer3 exposed on the bottom of the second connection hole 5. By removingthis native oxide film, the surface of the first conductive film layer 3is exposed. A second conductive film layer 7 is formed in a specifiedregion at least including the second connection hole 5 (FIG. 8C). Thesecond conductive film layer 7 is formed of an aluminum alloy film.

The second conductive film layer 7 is formed in a desired pattern by ananisotropic etching method such as RIE (FIG. 8D).

By this fabricating method, a two-layer wiring structure is realized.

Afterwards, a passivation film on the semiconductor element is formedwith a film thickness of 500 to 1200 nm.

In a semiconductor device fabricated by the conventional method,degradation phenomenon due to high temperature storage at 180° C. occursas explained below. A semiconductor device is fabricated for measuringthe degree of deterioration. The conditions with which the semiconductordevice is fabricated is explained below. As a first interlayerdielectric film layer 2, a BPSG film is deposited on the P-typesemiconductor substrate in a film thickness of 60 nm. A first conductivefilm layer 3 is deposited on the BPSG film. A second interlayerdielectric film layer 6 is formed thereon. A second connection hole 5 isformed in the second interlayer dielectric film layer 6. As a secondconductive film layer 7, an aluminum alloy film is deposited with a filmthickness of 1000 nm. As a passivation film, a PSG film having athickness of 300 nm and a silicon nitride film having a thickness of 800nm are formed.

FIG. 9 shows the relation between the contact hole size and the openfailure rate of a second connection hole.

As the high temperature storage time is increased to 180° C, the openfailure rate increases. After standing for 1600 hours, if the diameterof second connection hole 5 is smaller than about 1.4 μm, the openfailure rate increases suddenly. That is, in the prior art, although theconductive state is established immediately after manufacture, failurein the semiconductor device occurs by standing at a temperature of 180°C. When the diameter of the connection hole is smaller than a specificsize, open failure results, which poses a serious problem forreliability.

Thus, in the composition of the prior art, in a semiconductor devicewith multilayer wiring, when the diameter of the second connection hole5 becomes small, serious reliability problems result.

When multilayer wiring comprised of a fine dimensional structure ismanufactured in a semiconductor device of the prior art, in addition towiring breakage due to stress migration, open failure of connectionholes occurs, and a serious reliability problem takes place forconnection holes having a diameter of about 1.4 μm or less.

Failed semiconductor devices have been analyzed by use of a focused ionbeam (FIB) technique. As a result it was found that voids were formed inthe aluminum alloy film which is the second conductive film layer 7, atthe interface between the first conductive film layer 3 in the secondconnection hole 5 and the aluminum alloy film as the second conductivefilm layer 7. When voids are thus formed, the aluminum alloy film whichis the second conductive film layer 7 is eliminated. In this way, it wasdetermined that disconnection was the cause of the open failure.

The same problem occurs when copper elements are preliminarily added tothe aluminum alloy film.

The correlation between open failure rate and passivation film stresshave also been investigated in order to search the cause of openfailure. The stress of the passivation film was varied by the type ofthe passivation film. As a result of measurement of the semiconductordevice having a passivation film comprised of two layers of PSG film of300 nm in thickness and silicon nitride film of 800 nm in thickness, asemiconductor device having the passivation film comprised of a singlelayer of PSG film of 300 nm in thickness, a semiconductor device havinga passivation film composed of a single layer of silicon nitride of 800nm in thickness, and a semiconductor device without a passivation film,the PSG film formed by atmospheric pressure chemical vapor depositionmethod had a tensile stress of 2×10⁻⁹ dynes/cm² and the silicon nitridefilm formed by plasma enhanced chemical vapor deposition method had acompressive stress of 9×10⁻⁹ dynes/cm².

FIG. 10 shows the cumulative open failure of each semiconductor deviceafter high temperature storage at 180° C. in nitrogen atmosphere andafter standing for 1000 hours.

In a semiconductor device without passivation film, the cumulative openfailure was not increased, while a semiconductor device which is formedwith a silicon nitride film with a strong compressive stressdemonstrated an obvious increase in cumulative open failure.

In the prior art, the second conductive film layer 7 was formed bysputtering. Accordingly, in the second connection hole 5, the coverageof the second conductive film layer 7 is poor. Hence, the thickness ofthe second conductive film layer 7 in the second connection hole 5 isvery thin. Accordingly, due to the stress of the passivation film in theupper part, the aluminum atoms are moved, and voids are formed in thesecond connection hole 5, thereby easily leading to open failure.

As a method of improving the coverage of the second conductive filmlayer 7, the technique of burying the second connection hole 5 in aconductive film layer is known. For example, by burying tungsten, thecoverage of the second conductive film layer 7 in the second connectionhole 5 may be notably improved. In the case of tungsten burying,however, the resistance value of tungsten is increased by about ten-foldas compared with the case using the conventional aluminum alloy film.Due to such resistance increase, wiring delays occur, which may lead tooperating error of the semiconductor device. It is hence necessary toplan the design again by taking the resistance increase intoconsideration. Yet, the conventional design asset cannot be useddirectly.

The above problem, that is, occurrence of voids in the second connectionhole 5, may be easily avoided by forming the second conductive filmlayer 7 of a refractory metal such as tungsten. Since the melting pointis high in tungsten and other refractory metal, the wire is not easilybroken by the stress of the passivation film. However, tungsten andother refractory metals are higher in resistivity as compared withaluminum alloy film, and have increased wiring resistance.

It is hence an object of the invention to present a constitution inwhich the second conductive film layer is not moved easily by the stressof the upper passivation film. It is another object of the invention toprevent the occurrence of voids in the second connection hole. It is afurther object of the invention to suppress the increase of wiringresistance to a minimum. It is a further object of the invention topresent a semiconductor device particularly free from reliabilityproblems if the diameter of the connection hole in the multilayer wiringusing aluminum alloy film is smaller than about 1.4 μm. A manufacturingmethod is also disclosed.

SUMMARY OF THE INVENTION

In a semiconductor device, by using a barrier metal film in the firstconductive film layer, monocrystalline silicon precipitating in thecontact area of the aluminum alloy film and P-type semiconductorsubstrate is effectively prevented. Accordingly, the contact failure inthe contact area due to precipitation of monocrystalline silicon may beprevented. At the same time, aluminum spikes are not induced in thefirst connection hole due to mutual diffusion of the aluminum alloy filmand the silicon of P-type semiconductor substrate.

In addition, since a titanium film is used in the lower layer of thefirst conductive film layer, the nitrogen leaving the titanium nitridefilm of the intermediate layer is prevented from entering the aluminumalloy film. Hence, shortening of life due to electromigration of thealuminum alloy film may be prevented.

Moreover, since the titanium film of the upper layer and aluminum alloyfilm are alloyed, movement of aluminum atoms in the aluminum alloy filmmay be suppressed. By alloying both of them, in addition, grain growthin the aluminum alloy film may be suppressed. That is, occurrence ofvoids formed in the aluminum alloy film may be prevented. In addition,the resistance to stress migration may be enhanced.

There is an anti-reflection film in the upper layer of the firstconductive film layer, so that a photoresist pattern transferred as amask pattern may be formed in a specified region.

Of the second interlayer dielectric film layer, the silicon oxide filmof the lower layer prevents the first conductive film layer fromoxidizing by moisture of silicon oxide film as the intermediate layer.

Reversely, the silicon oxide film of the upper layer of the secondinterlayer dielectric film layer prevents moisture absorption of thesilicon oxide film of the intermediate layer.

Of the second interlayer dielectric film layer, the silicon oxide filmof the intermediate layer flattens the step difference of the firstconductive film layer, so that the second conductive film layer may notbe broken.

The semiconductor device of the invention is heat-treated and therefractory metal film of the second conductive film layer and thealuminum alloy film layer are alloyed, so that movement of aluminumatoms may be suppressed. In addition, since the refractory metal getsinto the aluminum alloy film by alloying, grain growth of aluminum alloyfilm inside may be suppressed. That is, formation of voids in thealuminum alloy film may be prevented. As a result, the resistance ofaluminum alloy film to stress migration may be improved.

In the semiconductor device of the invention, moreover, by forming arefractory metal in the lower layer of the second conductive film layer,movement of atoms composing the second conductive film layer of theupper layer by stress of the passivation film may be prevented, andoccurrence of voids in the second connection hole may be suppressed. Theincrease of wiring resistance may be kept to a minimum, and when appliedin the design model of the prior art, operating error in thesemiconductor device is not induced, and the design asset of the priorart may be directly utilized.

Further, in the semiconductor device of the invention, when the diameterof the second connection hole is greater than about 0.7 μm, the openfailure rate does not increase by high temperature storage at 180° C.

If the coverage of the aluminum alloy film in the second connection holeis poor, the open failure rate can be prevented.

The open failure rate may also be reduced by controlling the thicknessof the titanium film and diameter of the second connection hole.

Increase of the open failure rate may also be prevented in case of asilicon nitride film having a high stress directly on the secondconductive film layer as the passivation film.

In addition, titanium film is a metal with very high reactivity, andalloying is also promoted on the first conductive film layer formed inthe bottom of the second connection hole. Accordingly, when connectingthe first conductive film layer and the second conductive film layerthrough the second connection hole, contact failures are notablydecreased. Thus, the refractory metal film prevents formation of voidsin the aluminum alloy film, and by using titanium film as the refractorymetal film, contact failure in the second connection hole may bedecreased.

The titanium film is a highly reactive material, and the same effectsare obtained by the alloy film of titanium and other refractory metal(for example, the alloy film of titanium and tungsten).

According to the semiconductor device fabricating method of the presentinvention, since the second connection hole is formed by a combinationof isotropic etching and anisotropic etching, the wiring is not cut on astep in the connection hole.

After removing the native oxide film formed on the first conductive filmlayer by Argon back sputtering, the second conductive film layer isformed without being exposed to the atmosphere, so that the contact ofthe two is tight, and contact failure is avoided.

In addition, in the method of fabricating semiconductor devices of thepresent invention, since the refractory metal film is heat-treated toalloy also the first conductive film layer, the contact between thefirst conductive film layer and the second conductive film layer becomestighter. As a result, lowering of yield due to contact failure isprevented. At the same time, damage caused by etching may be recoveredby heat treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a semiconductor device of the presentinvention.

FIGS. 2A-D are process sectional views showing various steps in a methodof fabricating a semiconductor device according to the presentinvention.

FIG. 3 is a diagram showing the relation between the open failure rateand the size of a connection hole in accordance with the presentinvention.

FIG. 4 is a diagram showing the relation between the contact resistancevalue and the size of a connection hole in accordance with the presentinvention.

FIG. 5 is a diagram showing the dependence of open failure rate ontitanium film thickness in accordance with the present invention.

FIG. 6 is a diagram showing the relation between the storage time at180° C. and open failure rate in accordance with the present invention.

FIG. 7 is a diagram showing the yield for a semiconductor devicefabricated in accordance with the present invention as compared with theprior art.

FIGS. 8a through 8d are process sectional views.

FIG. 9 is a diagram showing the relation between the size of connectionholes and open failure rates in accordance with the prior art.

FIG. 10 is a diagram showing the dependence of cumulative open failurerate on the stress of passivation film in accordance with the prior art.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, an embodiment of the present invention isdescribed in detail below. FIG. 1 is a sectional view for explaining afirst embodiment of the semiconductor device of the present invention.

A semiconductor substrate with a first conductive type, for example, aP-type semiconductor substrate 21 is used. However, using an N-typesemiconductor substrate, the following description is quite the same. Inthe following explanation, it is assumed than any one of the ordinarysemiconductor elements of MOS transistors, MOS capacitors, bipolartransistors and resistors has been already formed on the P-typesemiconductor substrate 21 (not shown).

A first interlayer dielectric film layer 22 is formed on the P-typesemiconductor substrate 21. The first interlayer dielectric film layer22 is made of a BPSG film formed by a method of atmospheric pressurechemical vapor deposition.

Instead of the BPSG film, however, other dielectric films may be used,such as SiO₂ film and PSG film. The first interlayer dielectric filmlayer 22 is disposed in order to maintain the dielectric strengthbetween the semiconductor element formed in the P-type semiconductorsubstrate 21 and the first conductive film layer 23. The thickness ofthe first interlayer dielectric film layer 22 is about 400 to 1000 run.The first interlayer dielectric film layer 22 is disposed in order toimprove the step coverage of the first conductive film layer 23 formedthereon.

A first connection hole 24 is formed at a specified position of thefirst interlayer dielectric film layer 22. The first connection hole 24is formed in a shape so as not to break the upper first conductive filmlayer 23. That is, the shape of the first connection hole 24 is taperedso that the upper opening size of the first interlayer dielectric filmlayer 22 may be larger while the lower opening size may be smaller.

The first conductive film layer 23 is formed in a region at leastcontaining the first connection hole 24. The first conductive film layer23 is composed of three layers of a barrier metal film 23A, an aluminumalloy film 23B and an anti-reflection film 23C. The first conductivefilm layer 23 may also be composed of a single layer of aluminum alloyfilm alone, or two layers of barrier metal film and aluminum alloy film,or two layers of aluminum alloy film and anti-reflection film.

The first conductive film layer 23 is appropriately alloyed with theP-type semiconductor substrate 21. Accordingly, the contactcharacteristics are stabilized.

The thickness of the aluminum alloy film 23B is about 300 to 700 nm. Thealuminum alloy 23B is doped at least with an element for preventingmigration (e.g. Cu, Ti, Pd).

The aluminum alloy film 23B of this embodiment is doped with about 1.0%by mass of Si for preventing aluminum spikes and about 0.5% by mass ofCu for preventing migration.

The barrier metal film 23A is formed beneath the aluminum alloy film23B. At this time, the barrier metal film 23A brings about the followingaction. When the aluminum alloy film 23B and the P-type semiconductorsubstrate 21 contact with each other, monocrystalline siliconprecipitates. Such monocrystalline silicon increases the contactresistance value in the connection area between the aluminum alloy film23B and the P-type semiconductor substrate 21. By forming the barriermetal film 23A, an increase of the contact resistance value due toprecipitation of monocrystalline silicon is avoided in the firstconnection hole 24. It also prevents formation of aluminum spikes in thearea of the first connection hole 24 due to mutual diffusion of thealuminum alloy film 23B and silicon atoms of P-type semiconductorsubstrate 21. The barrier metal film 23A is composed of a titanium filmdeposited by sputtering and a titanium nitride film deposited byreactive sputtering. The thickness of the titanium film is about 10 to40 nm, and the thickness of the titanium nitride film is about 40 to 150nm.

The titanium film and the titanium nitride film of the barrier metalfilm 23A are formed by an inline method of sputtering. By inlinesputtering, the contact resistance value may be remarkably decreased bythe contact between the titanium film and the titanium nitride film,since the titanium nitride film is deposited on the titanium filmwithout forming native oxide on the titanium film.

The total thickness of the titanium film and the titanium nitride filmis about 50 to 190 nm. As the total thickness value is about 10% of thefirst interlayer dielectric film layer 22 in thickness, the stepcoverage of the aluminum alloy film 23B on the first connection hole 24is improved notably.

The barrier metal film 23A produces the same effects if composed ofrefractory metal, refractory silicide, refractory metal alloy or theirlaminate structure.

In addition, different effects are brought about when the barrier metalfilm 23A is composed of three layers of titanium film deposited bysputtering, titanium nitride film deposited by reactive sputtering, andtitanium film deposited by sputtering. At this time, the thickness ofthe lower titanium film is about 10 to 40 nm, the thickness of theintermediate titanium nitride film is about 40 to 150 nm, and thethickness of the upper titanium film is about 20 to 60 nm. By the uppertitanium film, invasion of nitrogen leaving the intermediate titaniumnitride film into the aluminum alloy film 23B is prevented. Wheninvasion of nitrogen into aluminum alloy film 23B is prevented,shortening of life of the aluminum alloy film 23B due toelectromigration may be avoided.

It is necessary to form the upper titanium film with a thickness of 20to 60 nm for prevention of nitrogen invasion into the aluminum alloyfilm 23B and electromigration of the aluminum alloy film 23B.

Furthermore, the upper titanium film and aluminum alloy film 23B arealloyed. This is effective to suppress the movement of aluminum atoms ofthe aluminum alloy film 23B. Furthermore, by alloying, titanium getsinto the aluminum alloy film 23B. Hence, grain growth in the aluminumalloy film 23B may be suppressed. That is, occurrence of voids in thealuminum alloy film 23B is prevented. In addition, the resistance tostress migration may be enhanced.

It is necessary to form the upper titanium film with a thickness of 20to 60 nm for increasing the resistance of stress migration.

Similar effects are obtained when the barrier metal film 23A is formedof an alloy film of titanium and tungsten deposited by sputtering. Thethickness of the alloy film of titanium and tungsten is about 40 to 150nm. When the barrier metal film 23A is formed of the alloy film oftitanium and tungsten, titanium and aluminum alloy film 23B are alloyed.As a result, titanium gets into the aluminum alloy film 23B.Consequently, movement of aluminum atoms of the aluminum alloy film 23Bis suppressed. It is also possible to suppress grain growth in thealuminum alloy film 23B. That is, occurrence of voids in the aluminumalloy film 23B may be prevented. Thus, the resistance to stressmigration may be enhanced.

The anti-reflection film 23C is formed on the aluminum alloy film 23B.The anti-reflection film 23C reduces the surface reflectivity of thefirst conductive film layer 23. Usually, when processing the firstconductive film layer 23 into a desired shape by RIE, a pattern ofphotoresist is formed in the specified region. The photoresist patternis formed by a reduced projection exposure method. By the light from thereduced projection exposure apparatus, the photoresist pattern isprojected on the photoresist and sensitized. At this time, if there is amaterial of high surface reflectivity such as the aluminum alloy film23B, and having a step difference beneath the aluminum alloy film 23B,the photoresist is sensitized as follows. The photoresist is sensitizednot only by the light from the reduced projection exposure apparatus butalso by the light reflected by the aluminum alloy film 23B in the matrixafter penetrating through the photoresist. Accordingly, the desiredpattern on the photomask cannot be projected precisely on thephotoresist. Therefore, the anti-reflection film 23C is formed on theentire surface of the aluminum alloy film 23B. By reducing the surfacereflectivity, sensitization of the photoresist by the light reflectedfrom the matrix may be decreased. As a result, the desired patternformed on the photomask may be precisely transferred on the photoresist.Using the anti-reflection film 23C, the pattern of the photoresistformed may be also transferred at high precision when opening the secondconnection hole 25 by anisotropic etching (such as RIE).

The anti-reflection film 23C is formed of a titanium nitride filmdeposited by reactive sputtering. The thickness of the titanium nitridefilm is about 20 to 60 nm. The same effects will be obtained if theanti-reflection film 23C is composed of refractory metal film orrefractory metal silicide film or an alloy film of refractory metal.

As mentioned above, all of the barrier metal film 23A, the aluminumalloy film 23B, and anti-reflection film 23C are formed using the samesputtering method. Since each of these films are reactive for thechemical characteristics, oxide films on the surface of these films areformed by contact air. The contact resistance is increased by the oxidefilms. So it is desirable that the films of the barrier metal film 23A,the aluminum alloy film 23B, and the anti-reflection film 23C are formedusing inline sputtering.

A second interlayer dielectric film layer 26 is formed on the firstconductive film layer 23 formed in a desired shape. The secondinterlayer dielectric film layer 26 is composed of a lower layer ofsilicon oxide film 26A, an intermediate layer of silicon oxide film 26Busing inorganic silica or organic silica, and an upper layer of siliconoxide film 26C. The lower layer of silicon oxide film 26A is formed byapplying a high frequency in a vapor phase containing, for example, SiH₄or TEOS (tetraethylorthosilicate). It is deposited by the so-calledplasma enhanced chemical vapor deposition method.

The intermediate layer of silicon oxide film 26B is an inorganic silicaor organic silica in gel form. The silica is applied on the siliconoxide film 26A by spinning, and baked. The silicon oxide film 26C isformed, as is the silicon oxide film 26A, by a method of plasma enhancedchemical vapor deposition. In this way, the second interlayer dielectricfilm layer 26 is composed of three layers, the silicon oxide films 26A,26B, 26C.

Of the second interlayer dielectric film layer 26, the lower siliconoxide film 26A contacts with the first conductive film layer 23 and thesilica of the silicon oxide film 26B. The lower silicon oxide film 26Aprevents oxidation of the first conductive film layer 23 by the moisturecontained in the silica when forming the silicon oxide film 26B. Theintermediate silicon oxide film 26B flattens the step difference of thefirst conductive film layer 23. That is, the surface of the uppersilicon oxide film 26C is flattened. This helps to prevent breakdown ofthe second conductive film layer 27 formed on the silicon oxide film 26Cin later processing due to its step difference. The upper silicon oxidefilm 26C adds to the film strength of the second interlayer dielectricfilm layer 26 itself. The top silicon oxide film 26C also protects thesurface of the intermediate silicon oxide film 26B. The top siliconoxide film 26C further prevents the silicon oxide film 26B fromabsorbing moisture.

The thickness of the silicon oxide film 26A is about 100 to 400 nm.

For preventing moisture contained in the intermediate silicon oxide film26B arriving at the surface of the first conductive film layer 23, it isimportant that the thickness of the lower silicon oxide film 26A isabout 100 to 400 nm by the method of plasma enhanced chemical vapordeposition using gas which includes TEOS.

The thickness of the silicon oxide film 26B is about 150 to 250 nm. Thethickness of the silicon oxide film 26C is about 200 to 500 nm. It isappropriate that the thickness of the upper silicon oxide film 26C isabout 200 to 500 nm for mechanical strength in protecting the lowersilicon oxide film 26B. The total film thickness of the secondinterlayer dielectric film layer 26 is about 500 to 1000 nm.

By using the total film thickness of the second interlayer dielectricfilm layer 26, insulation between the first conductive film layer 23 andthe second conductive film layer 27 is achieved.

A second connection hole 25 is formed at a specified position of thesecond interlayer dielectric film layer 26. The second connection hole25 is designed to prevent disconnection of the second conductive filmlayer 27 formed as the upper layer in a later process. That is, the holeis tapered so that the upper opening size of the second interlayerdielectric film layer 26 may be larger while the lower opening size maybe smaller.

A second conductive film layer 27 is formed in a region at leastcontaining the second connection hole 25. The second conductive filmlayer 27 is composed of two layers of a bottom refractory metal film 27Aand a top aluminum alloy film 27B. The second conductive film layer 27is formed in a greater thickness than the first conductive film layer 23in order to lessen the step difference of the multilayer wiring.

While the refractory metal film 27A and the aluminum alloy film 27B ofthe second conductive film layer 27 are active for the chemicalcharacteristics, oxide films on the surface of these films are formed bycontact air. The contact resistance is increased by the oxide films.When forming these film, it is important to use inline sputtering.

The refractory metal film 27A and the aluminum alloy film 27B as thesecond conductive film layer 27 are alloyed. Accordingly, movement ofaluminum atoms of the aluminum alloy film 27B may be suppressed. Byalloying, the refractory metal gets into the aluminum alloy film 27B.The refractory metal will suppress grain growth of the aluminum alloyfilm 27B inside. As a result, occurrence of voids in the aluminum alloyfilm 27B may be prevented. Hence, the resistance of the aluminum alloyfilm 27B to stress migration may be enhanced. Furthermore, therefractory metal film 27A is also alloyed with the first conductive filmlayer 23. As a result, the contact of the first conductive film layer 23and the second conductive film layer 27 is tighter. Consequently,lowering of yield due to contact failure is prevented.

In order that voids may not be occurred in the aluminum alloy film 27B,the refractory metal film 27A of the bottom layer and aluminum alloyfilm 27B are alloyed. Thus, by alloying, the refractory metal atoms getinto the aluminum alloy film. As a result, it is effective to suppressmovement of aluminum atoms induced by the stress of the passivationfilm.

The thickness of the aluminum alloy film 27B is about 700 to 1200 nm.The aluminum alloy film 27B is, as with the aluminum alloy film 23B,doped at least with elements for preventing migration (e.g. Cu, Ti, Pd).The aluminum alloy film 27B used in this embodiment is doped with about1.0% by mass of Si for preventing aluminum spikes, and about 0.5% bymass of Cu for preventing migration.

The refractory metal film 27A is formed beneath the aluminum alloy film27B. The refractory metal film 27A is formed in order to preventoccurrence of voids in the aluminum alloy film 27B. The refractory metalfilm 27A is composed of a titanium film deposited by sputtering. Thethickness of the titanium film is about 30 to 150 nm.

Since the second conductive film 27 is composed of two layers oftitanium film and aluminum alloy film 27B, the titanium film andaluminum alloy film 27B are alloyed. It helps to suppress movement ofaluminum atoms inside of the aluminum alloy film 27B. It is alsoeffective to suppress grain growth of the aluminum alloy film 27B as thetitanium gets into the crystal grain boundary of the aluminum alloy film27B. That is, formation of voids inside the aluminum alloy film 27B issuppressed. In addition, the resistance of the aluminum alloy film 27Bto stress migration may be enhanced.

The refractory metal film 27A may also be composed of other refractorymetals (W, Mo, Ta, Hf, etc.), refractory metal compound, refractorymetal silicide, or alloy of refractory metals. Likewise, formation ofvoids inside the aluminum alloy film 27B may be prevented. Therefractory metal film 27A is appropriately alloyed with the upperaluminum alloy film 27B in subsequent heat treatment. By alloying, graingrowth of aluminum alloy film may be suppressed. Thus, by using thematerial suppressing the grain growth more efficiently, the growth ofvoids formed in the aluminum alloy film may be suppressed. It is moreeffective for enhancement of resistance to stress migration.

FIGS. 2A-D are process sectional views for explaining a first embodimentof the present invention relating to a method of fabricating asemiconductor device.

As the semiconductor substrate of the first conductive type, forexample, the P-type semiconductor substrate 21 is used in the followingdescription. The following description is also applicable to the use ofan N-type semiconductor substrate. It is assumed in the followingexplanation that any one of the ordinary semiconductor elementsincluding a MOS transistor, a MOS capacitor, a bipolar transistor and aresistor has been already formed on the P-type semiconductor substrate21 (not shown).

A first interlayer dielectric film 22 is formed on the P-typesemiconductor substrate 21. A silicon oxide film formed by low pressurechemical vapor deposition or atmospheric pressure chemical vapordeposition may be used. As the silicon oxide film, for example, a BPSGfilm formed by atmospheric pressure chemical vapor deposition method isused. Instead of BPSG film, however, the silicon oxide film may also becomposed of SiO₂ film, PSG film and other dielectric films. The firstinterlayer dielectric film layer 22 is intended to maintain dielectricstrength between the semiconductor element formed on the P-typesemiconductor substrate 21, and the first conductive film layer 23. Thethickness of the first interlayer dielectric film layer 22 is about 400to 1000 nm. The first interlayer dielectric film 22 is disposed in orderto improve the step coverage of the first conductive film layer 23formed thereon. That is, by heat treatment and flowing of the firstinterlayer dielectric film layer 22, the surface of the first conductivefilm layer 23 is flattened. For flowing, the temperature of heattreatment is as high as 850 to 950° C., which is carried out in nitrogengas atmosphere, or mixed gas atmosphere of hydrogen and oxygen. Byflowing in a mixed gas atmosphere of hydrogen and oxygen, the surface isflattened more smoothly than flowing in a nitrogen gas atmosphere.

Next, by selectively removing the specified position of the firstinterlayer dielectric film layer 22, a first connection hole 24 isformed. The first connection hole 24 is formed so as not to break theupper first conductive film layer 23. When etching the upper part of thefirst interlayer dielectric film layer 22, isotropic etching such as wetetching is employed. After etching of the upper part, when etching theremaining first interlayer dielectric film layer 22 (lower part),anisotropic etching such as reactive ion etching (RIE) is employed. Inthis way, the first connection hole 24 is formed. The shape of the firstconnection hole 24 is tapered so that the upper opening size of thefirst interlayer dielectric film layer 22 may be larger while the loweropening size may be smaller. If such a shape may be realized, the firstconnection hole 24 may be formed only by anisotropic etching (FIG. 2A).

After etching, a native oxide film is formed on the exposed P-typesemiconductor substrate 21.

The native oxide film on the P-type semiconductor substrate 21 exposedto the bottom of the first connection hole 24 is removed, for example,by a diluting solution such as hydrofluoric acid. Later, the firstconductive film layer 23 is formed. The first conductive film layer 23is composed of three layers of a barrier metal film 23A, an aluminumalloy film 23B, and an anti-reflection film 23C. The first conductivefilm layer 23 may also be composed of a single layer of aluminum alloyfilm alone, or two layers of barrier metal film and aluminum alloy film,or two layers of aluminum alloy film and anti-reflection film. The firstconductive film layer 23 is processed into a desired pattern byanisotropic etching such as RIE.

Afterwards, for example, in a hydrogen gas atmosphere, or in a mixed gasatmosphere of hydrogen and nitrogen, heat treatment is conducted at thetemperature of about 450° C. By this heat treatment, the firstconductive film layer 23 and silicon atoms of the P-type semiconductorsubstrate 21 are properly alloyed. As a result, the contactcharacteristics are stabilized. Further, by this heat treatment, thedamage caused by anisotropic etching such as RIE is recovered (FIG. 2B).

The aluminum alloy film 23B is formed by sputtering. At this time, thefilm thickness is about 300 to 700 nm. The aluminum alloy film 23B isdoped at least with elements for preventing migration (Cu, Ti, Pd,etc.).

The aluminum alloy film 23B of the embodiment is doped with about 1.0%by mass of Si for preventing aluminum spike, and about 0.5% by mass ofCu for preventing migration.

The barrier metal film 23A is formed beneath the aluminum alloy film23B.

By forming the barrier metal film 23A, an increase of contact resistancevalue due to precipitation of single crystalline silicon in the firstconnection hole 24 is avoided. Formation of aluminum spikes in the firstconnection hole 24 due to mutual diffusion of the aluminum alloy film23B and silicon atoms of P-type semiconductor substrate 21 is alsoprevented. The barrier metal film 23A is composed of two layers of atitanium film deposited by sputtering and a titanium nitride filmdeposited by reactive sputtering. The film thickness of titanium film isabout 10 to 40 nm, and the titanium nitride film is formed with athickness of about 40 to 150 nm.

The barrier metal film 23A provides the same effects when composed ofrefractory metal, refractory metal silicide, refractory metal compound,or their stacked structure.

The barrier metal film 23A brings about different effects when composedof three layers of a titanium film deposited by sputtering, a titaniumnitride film deposited by reactive sputtering, and a titanium filmdeposited by sputtering. At this time, the thickness of the lower layerof the titanium film is about 10 to 40 nm, the thickness of theintermediate layer of the titanium nitride film is about 40 to 150 nm,and the thickness of the upper titanium film is about 20 to 60 nm. Bythe titanium film of the top layer, the nitrogen leaving theintermediate titanium nitride film is prevented from entering thealuminum alloy film 23B. When entry of nitrogen into the aluminum alloyfilm 23B is prevented, shortening of life of the aluminum alloy film 23Bdue to electromigration may be prevented.

Furthermore, the titanium film of the upper layer and the aluminum alloyfilm 23B are alloyed. Accordingly, movement of aluminum atoms in thealuminum alloy film 23B is suppressed. By alloying, moreover, occurrenceof voids in the aluminum alloy film 23B may be prevented. In addition,the resistance to stress migration may be enhanced.

Similar effects are produced when the barrier metal film 23A is composedof an alloy film of titanium and tungsten deposited by sputtering. Thethickness of the alloy film of titanium and tungsten is about 40 to 150nm. When the barrier metal film 23A is formed from the alloy film oftitanium and tungsten, the titanium and the aluminum alloy film 23B arealloyed. As a result, the titanium atoms get into the aluminum alloyfilm 23B. Hence, the resistance to stress migration may be enhanced.

The anti-reflection film 23C is formed on the aluminum alloy film 23B.The anti-reflection film 23C decreases the surface reflectivity of thefirst conductive film 23.

The anti-reflection film 23C is formed of a titanium nitride filmdeposited by reactive sputtering. The thickness of the titanium nitridefilm is about 20 to 60 nm. The anti-reflection film 23C produces similareffects if composed of a refractory metal film, refractory metalsilicide film, or alloy film of refractory metal.

In succession, a second interlayer dielectric film layer 26 is formed onthe first conductive film layer 23 in a specified pattern. The secondinterlayer dielectric film layer 26 is composed of a lower layer ofsilicon oxide film 26A, an intermediate layer of silicon oxide film 26Busing inorganic silica or organic silica, and a upper layer of siliconoxide film 26C. The lower silicon oxide film 26A is formed by applyinghigh frequency in a vapor phase containing, for example, SiH₄ or TEOS(tetraethylorthosilicate). It is deposited by the so-called plasmaenhanced chemical vapor deposition method.

The intermediate silicon oxide film 26B is organic silica or inorganicsilica in gel form. The silica is applied on the silicon oxide film 26Aby spinning, and baked. The silicon oxide film 26C is formed by theplasma enhanced chemical vapor deposition method as with the siliconoxide film 26A.

Of the second interlayer dielectric film layer 26, the lower siliconoxide film 26A contacts with the first conductive layer 23 and thesilica of the silicon oxide film 26B. The lower silicon oxide film 26Aprevents oxidation of the first conductive film layer 23 by the moisturecontained in silica when forming the silicon oxide film 26B. Theintermediate silicon oxide film 26B flattens the step difference of thefirst conductive film layer 23 of the matrix. That is, the surface ofthe upper silicon oxide film 23C is flattened. Accordingly, in the laterprocess, the second conductive film layer 27 formed on the silicon oxidefilm 26C is prevented from being broken due to a step difference. Theupper silicon oxide film 26C adds to the strength of the secondintermediate insulation film layer 26 itself. It further protects thesurface of the intermediate silicon oxide film 26B. It moreover preventsmoisture absorption of the silicon oxide film 26B.

The thickness of the silicon oxide film 26A is about 100 to 400 nm. Thesilicon oxide film 26B is formed by repeating the spinning applicationprocess of silica and baking process several times at a temperature ofabout 450° C. The thickness of the silicon oxide film 26B is about 150to 250 nm. The thickness of the silicon oxide film 26C is about 200 to500 nm. Finally, the total thickness of the second interlayer dielectricfilm layer 26 is about 500 to 1000 nm.

Any one of the three silicon oxide films 26A, 26B, 26C composing thesecond interlayer dielectric film layer 26 may be a silicon oxide filmformed by the following method. For example, in a vapor phase containingat least TEOS, after thickly depositing the silicon oxide film by theplasma enhanced chemical vapor deposition method by applying a highfrequency signal, the entire surface is etched to form a silicon oxidefilm in a specified thickness. Or, the silicon oxide film may be formedby pyrolysis of mixed gas of ozone and TEOS.

A specified position of the second interlayer dielectric film layer 26is removed selectively. The removed region becomes a second connectionhole 25. The second connection hole 25 is intended to prevent breakdownof the second conductive film layer 27 formed in the upper part in alayer process. That is, the upper region of the second interlayerdielectric film layer 26 is formed by isotropic etching such as wetetching. Later, the lower region is formed by anisotropic etching suchas RIE (reactive ion etching). As a result, the hole is formed in ataper so that the upper opening size of the second interlayer dielectricfilm layer 26 may be large while the lower opening size may be small. Ifformed in such a shape, the second connection hole 25 may be formed byanisotropic etching only.

After forming the second connection hole 25, heat treatment is appliedat a temperature of about 380° C. By this heat treatment, the damage byetching may be recovered. Furthermore, the silicon oxide film 26Bexposed on the side wall of the second connection hole 25 may be bakeduntil solid (FIG. 2C).

By forming the second connection hole 25, a native oxide film,especially aluminum oxide (Al₂ O₃) is formed on the first conductivefilm 23 layer on the exposed surface. It is removed by sputtering usingargon ions. At this time, the pressure of argon gas is about 5 mtorr.

Removal of the native oxide film is intended to tighten the contactbetween the first conductive film layer 23 exposed to the lower of thesecond connection hole 25 and the second conductive film layer 27,thereby avoiding contact failure.

The process of removing the native oxide film on the first conductivefilm layer 23 is not limited to the sputtering method using argon, butany other method may be employed as long as the native oxide film on thefirst conductive film layer 23 can be removed. For example, RIE usingreactive gas may be employed.

The second conductive film layer 27 is formed without exposing thesurface of the thus obtained clean first conductive film layer to theair.

The second conductive film layer 27 is composed of two layers, usingrefractory metal film 27A in the bottom layer, and the aluminum alloyfilm 27B in the top layer. The second conductive film layer 27 is formedin a greater thickness than the first conductive film layer 23 in orderto lessen the step difference of the multilayer wiring.

Afterwards, the second conductive film layer 27 is formed in a specifiedshape by anisotropic etching such as RIE.

Next, for example, in hydrogen gas atmosphere, or in a mixed gasatmosphere of hydrogen and nitrogen, heat treatment is conducted at atemperature of about 450° C. By heat treatment, the refractory metalfilm 27A and aluminum alloy film 27B composing the second conductivefilm layer 27 are alloyed. It is accordingly effective to suppress themovement of aluminum atoms of the aluminum alloy film 27B. By alloying,moreover, the refractory metal atoms get into the aluminum alloy film27B. In the presence of refractory metal film 27A, grain growth ofaluminum alloy film 27B inside may be suppressed. As a result, formationof voids in the aluminum alloy film 27B is prevented. Hence, theresistance of aluminum alloy film 27B to stress migration is enhanced.Furthermore, by heat treatment, the refractory metal film 27A alsoalloys the first conductive film layer 23 exposed to the bottom of thesecond connection hole 25. Accordingly, lowering of yield due to contactfailure may be prevented. Besides, the damage caused by anisotropicetching such as RIE may be recovered by heat treatment (FIG. 2D).

In order to prevent formation of voids in the aluminum alloy film 27B,the refractory metal film 27A of the bottom layer and aluminum arealloyed. By alloying, as mentioned above, the refractory metal atoms getinto the aluminum alloy film. It hence suppresses movement of aluminumatoms induced by the stress of the passivation film. For the ease ofexpression of this effect, alloying of the bottom refractory metal 27Aand top aluminum alloy film 27B is made uniform. For this purposeformation of the interface layer that may impede alloying is prevented,in the interface of the aluminum alloy film 27B and refractory metalfilm 27A. What may become an interface layer in the hitherto process is,for example, the oxide layer of refractory metal film. Therefore,depositing of refractory metal film 27A and depositing of aluminum alloyfilm 27B are done continuously without being exposed to the atmosphere.By forming them continuously, occurrence of voids inside of the aluminumalloy film 27B may be suppressed.

The aluminum alloy film 27B may be formed by sputtering. Its filmthickness is about 700 to 1200 nm. The aluminum alloy film 27B is doped,at least, with elements for preventing migration (Cu, Ti, Pd), as withthe aluminum alloy film 23B. The aluminum alloy film 27B used in thisembodiment is doped with about 1.0% by mass of Si for preventingaluminum spikes, and about 0.5% by mass of Cu for preventing migration.

The refractory metal film 27A is formed beneath the aluminum alloy film27B. The aluminum alloy film 27A is formed in order to prevent formationof voids in the aluminum alloy film 27B. The refractory metal film 27Ais composed of a titanium film deposited by sputtering. The thickness ofthe titanium film is about 30 to 100 nm.

When the second conductive film layer 27 is composed of two layers oftitanium film and aluminum alloy film 27B, the titanium film andaluminum alloy film 27B are alloyed. Thus, movement of aluminum atomsinside of the aluminum alloy film 27B may be suppressed. In addition,the titanium atoms get into the crystal grain boundary of the aluminumalloy film 27B, thereby suppressing the grain growth of the aluminumalloy film 27B. That is, formation of voids inside the aluminum alloyfilm 27B may be prevented. In addition, the resistance of the aluminumalloy film 27B to stress migration may be enhanced.

The refractory metal film 27A may be composed also of other refractorymetal (W, Mo, Ta, Hg, etc.), refractory metal compound, refractory metalsilicide, or an alloy of refractory metals. Similarly, occurrence ofvoids inside the aluminum alloy film 27B may be prevented. Moreover, therefractory metal film 27A and the aluminum alloy film 27B of the toplayer are appropriately alloyed by later heat treatment. By alloying,grain growth of aluminum alloy film is suppressed. Thus, by using amaterial suppressing the grain growth, the occurrence of voids formed inthe aluminum alloy film may be suppressed more effectively. It is thusmore effective for the enhancement of resistance of stress migration.

In succession, usually, the passivation film is formed. The passivationfilm is composed of PSG film and silicon nitride film. Th PSG filmrelaxes the high stress of the silicon nitride film. The stress ofsilicon nitride film induces breakdown of the second conductive filmlayer 27. The PSG film is formed, for example, by the method ofatmospheric pressure chemical vapor deposition. The thickness of PSGfilm is about 100 to 400 nm. The silicon nitride film prevents moistureand pollutants from getting inside. The silicon nitride film is formed,for example, by the method of plasma enhanced chemical vapor deposition.The thickness of silicon nitride film is about 500 to 1200 nm (notshown).

FIG. 3 shows the results of reliability tests of the second connectionhole of the semiconductor device fabricated according to thisembodiment.

The semiconductor device in the test is composed as follows. On a 6-inchP-type semiconductor substrate, a BPSG film of 600 nm in thickness isdeposited. On the BPSG film, a barrier metal film and an aluminum alloyfilm are deposited as a first conductive film layer. The barrier metalfilm is composed of two layers of titanium film and titanium nitridefilm. The thickness of titanium film is 20 nm, and the thickness oftitanium nitride film is 100 nm. The aluminum alloy film is doped with1.0% by mass of silicon and 0.5% by mass of copper. The thickness ofaluminum alloy film is 600 nm. A second interlayer dielectric film iscomposed of a silicon oxide film in a film thickness of 400 nm, asilicon oxide film of inorganic silica or organic silica in gel form,and a silicon oxide film in a film thickness of 300 nm. A secondconductive film layer is composed of a titanium film in a thickness of50 nm, and an aluminum alloy film in a thickness of 1000 nm. Apassivation film is composed of a PSG film in a thickness of 300 nm anda silicon nitride film in a thickness of 800 nm.

On the thus composed P-type semiconductor substrate, 100,000 secondconnection holes are disposed in series. A total of 120 contact chainsof the first conductive film layer and second conductive film layer areformed.

In composing the sample, what is different from the prior art is thatthe second conductive film layer is composed of two layers of titaniumfilm and aluminum alloy film.

FIG. 3 shows the results of open failure rate of the contact chains ofthis semiconductor device by investigating the electrical conductingstate. The axis of abscissas denotes the contact hole size or thediameter of the second connection holes. The axis of ordinatesrepresents the open failure rate. The open failure rate right aftermanufacture is indicated by an arrow with the term "initial" in thediagram. The other curves are obtained at different high temperaturestorage durations at 180° C. in a nitrogen atmosphere. The hightemperature storage durations are 400 hours, 800 hours and 1600 hours,and the open failure rate after letting the semiconductor device standfor each duration is shown. As known therefrom, when the diameter of thesecond connection holes is greater than about 0.6 μm, the open failurerate caused by high temperature storage at 180° C. does not increase,unlike the prior art shown in FIG. 8. That is, by forming the titaniumfilm in the bottom layer of the second conductive film, the open failurerate was lowered as compared with the prior art. At this time, if thetitanium film is formed in the bottom layer of the aluminum alloy film,the coverage of aluminum alloy film in the second connection hole is notimproved. In the diagram, however, even in the positions where thethickness of the second conductive film layer is very thin, the openfailure rate is lower than in the prior art. This fact suggests thatvoids are not formed in the aluminum alloy film of the top layer of thesecond conductive film layer in the second connection hole. That is,occurrence of voids is suppressed. Even in the contact hole side fallinginto open failure due to growth of voids in the prior art, open failuresare not witnessed in the embodiment. In the prior art, when the contacthole size is smaller than 1.4 μm, a problem arises in the reliability ofsemiconductor devices. In this embodiment, by contrast, as long as thecontact hole size is greater than 0.6 μm, no adverse effect is caused tothe reliability of the semiconductor device. In this embodiment,lowering of reliability of the semiconductor device by formation ofvoids may be prevented.

FIG. 4 shows the relation between the contact hole size and contactresistance.

This study uses the same samples which were used in FIG. 3. However, thetitanium film was used in the refractory metal film in the bottom layerwhich is the second conductive film layer, and the thickness of thetitanium film was 10 nm, 30 nm, and 50 nm, and the resistance of thecontact chain was measured.

The contact resistance was expressed by the value of resistance per onesecond connection hole by dividing the total resistance value of thecontact chain by 10,000 (or the number of contacts).

The contact chain resistance is compared between the prior art and thisembodiment. In this embodiment, the thickness of the titanium film asthe second conductive film layer is 50 nm. In the prior art, withouttitanium film, the aluminum alloy film in a thickness of 1000 nm wasused as the second conductive film layer. The contact resistance of thisembodiment at this time was about 30 to 40% higher than that of theprior art.

The resistance of the contact chain approaches the resistance of theconventional constitution when the thickness of the titanium filmbecomes smaller than 50 nm. When the thickness of the titanium film isgreater than 50 nm, the contact resistance further increases. On theother hand, to suppress the formation of voids in the second connectionholes, it is more advantageous when the thickness of the titanium filmis greater.

FIG. 5 shows the relation between the contact hole size and the openfailure rate at the titanium film in 10 nm, 30 nm, and 50 nmthicknesses. The contact hole indicates the diameter of the secondconnection holes. In this study, all samples were carried out at hightemperature storage for 1000 hours at 180° C. in a nitrogen atmosphere.The diagram also shows the result of the prior art without titaniumfilm.

When the thickness of titanium film is 30 nm, the diameter of the secondconnection holes at which the open failure rate begins to increase isgreater than that when the thickness of titanium film is 50 nm. That is,when the thickness of titanium film is 30 nm, the open failure ratebegins to increase at the diameter of the second connection holes ofabout 0.7 μm, while in the case of titanium film in 50 nm thickness, itis about 0.6 μm. Similarly, a more obvious difference is noted at thetitanium film in 10 nm thickness.

Therefore, in the state of maintaining the reliability of finer secondconnection holes, if an attempt is made to suppress the increase ofwiring resistance, it is necessary to select the titanium film having aproper thickness depending on the semiconductor device. For example,when manufacturing a semiconductor device for which the diameter ofsecond connection holes is 1.0 μm, for an aluminum alloy film in athickness of 700 to 1200 nm, a titanium film in 50 nm thickness shouldbe used as the second conductive film layer.

FIG. 6 shows the relation between the open failure rate and the time ofleaving the semiconductor device in nitrogen atmosphere at thetemperature of 180° C. The result suggests that the open failure ratefor disconnection varies due to occurrence of voids inside the secondconductive film layer. This change of open failure rate means thetransitional change of the open failure rate when leaving thesemiconductor device at the temperature of 180° C.

The diagram discloses a case using a single layer of aluminum alloy filmin the prior art and a case of the aluminum alloy film depositedtitanium film as the bottom layer in this embodiment.

In the sample of the invention, the second conductive film layer iscomposed of titanium film in 50 nm thickness and aluminum alloy film in1000 nm thickness. The second conductive film layer is 0.8 μm in wirewidth and 60 cm in wiring length. A total of 267 pieces of such apattern were fabricated on the 6-inch P-type semiconductor substrate,and the electric conductive state was investigated, and the open failurerate was calculated. In addition, for the ease of forming voids on thealuminum alloy film as the second conductive film layer of thesemiconductor device, a silicon nitride film with a high stress isusually formed as passivation film directly on the second conductivefilm layer. The silicon nitride film is formed in 800 nm thickness bythe method of plasma enhanced chemical vapor deposition.

As shown in FIG. 6, in the single layer of aluminum alloy film, as thestorage time at the temperature of 180° C becomes longer, the openfailure rate of the semiconductor device increases. This means that thevoids formed in the aluminum alloy film grow as the storage time passes.By growth of voids, the wire breakdown is likely to occur, and the openfailure rate increases. By contrast, by depositing titanium film whichis a refractory metal in the bottom layer of the second conductive filmlayer, it is known that voids are not formed in the aluminum alloy filmof the top of the second conductive film layer. Even after letting thesemiconductor device stand for 3000 hours, the second conductive filmlayer is not broken, and the open failure rate does not elevate. Thus,by depositing the titanium film in the bottom layer, the reliability ofsecond connection holes is improved, and the resistance of the secondconductive film layer which is the aluminum alloy film to stressmigration is enhanced at the same time.

Furthermore, since titanium film is a very reactive metal, alloying isalso promoted on the first conductive film layer formed on the bottom ofthe second connection holes. As a result, the contact failures aredecreased notably when connecting the first conductive film layer andsecond conductive film layer through the second connection holes. Thus,the refractory metal film is capable of preventing formation of voids inthe aluminum alloy film, and by titanium film as the refractory metalfilm, furthermore, contact failures in the second connection holes maybe reduced.

The titanium film is a highly reactive material, and the same effectsare obtained by an alloy film of titanium and other refractory metal,for example, an alloy film of titanium and tungsten.

As, therefore, titanium film is reactive for the chemicalcharacteristics, the titanium and the first conductive film layer 27 atthe bottom of the second connect hole 25 are promoted to alloy. Thus,contact failure of first conductive film layer 23 and second conductivefilm layer 27 are decreased remarkably.

FIG. 7 is a diagram showing the yield of a semiconductor devicefabricated in accordance with the present invention as compared with theprior art. Semiconductor devices with 900,000 second connection holes ina chip of 30 mm² area are fabricated on a 6 inch semiconductorsubstrate. FIG. 7 is a diagram showing the yield for substrates ofvarious numbers. Yields of semiconductor devices fabricated with theprior art are shown relative to substrate numbers 1 to 8. The substratesnumbered 9 to 16 are yields of semiconductor deviced fabricatedaccording to the present invention. The yield is higher forsemiconductor devices formed in accordance with the present inventionthan for semiconductor devices formed in accordance with the prior art.This suggests that the reliability of semiconductor devices which arefabricated in accordance with the present invention are superior to thatof the prior art. That is, titanium film of refractory metal filmbeneath the second conductive film layer may prevent occurrence of voidsin aluminum alloy film and result in a decrease in the contact failurerate in second connection holes.

Thus, by composing the second conductive film layer of two layers ofrefractory metal and aluminum alloy film, formation of voids in thealuminum alloy film may be suppressed. As a result, the reliability ofthe finer second connection holes (as compared with the prior art) maybe maintained. In addition, the wiring density of semiconductor devicesmay be greatly raised. That is, in an area smaller than in the priorart, a semiconductor device with equivalent functions may be fabricated.Furthermore, without increasing the chip size, a semiconductor devicehaving higher functions may be fabricated. By using titanium film oralloy film of titanium and tungsten as the refractory metal, moreover,it is possible to more tightly connect with the first conductive filmthan in the prior art. Hence, the semiconductor devices may bemanufactured at a higher successful rate than in the prior art.

What is claimed:
 1. A method of fabricating a semiconductor devicecomprising:a step of forming a first interlayer dielectric film layer ina first region on a semiconductor substrate, a step of forming firstconnection holes for exposing the semiconductor substrate in the firstinterlayer dielectric film layer, a step of removing a first oxide filmfrom the exposed surface of the semiconductor substrate, a step offorming a first conductive film layer on the exposed surface of thesemiconductor substrate and on the first interlayer dielectric filmlayer, a step of forming a second interlayer dielectric film layer onthe first conductive film layer, a step of forming second connectionholes for exposing the first conductive film layer in the secondinterlayer dielectric film layer, a step of removing a native oxide filmfrom the exposed surface of the first conductive film layer, and a stepof forming a second conductive film layer on the exposed surface of thefirst conductive film layer and on the second interlayer dielectric filmlayer without exposing to air, wherein the first conductive film layercomprises a barrier metal film, an anti-reflection film and a firstaluminum alloy film, the second conductive film layer consists of arefractory metal film from 30 nm to 150 nm thick and a second aluminumalloy film formed on the refractory metal film, and forming of therefractory metal film and forming of the second aluminum alloy film aredone continuously without being exposed to atmosphere, and wherein theanti-reflection film is formed on the first aluminum alloy film and thefirst aluminum alloy film is then exposed by the second connectionholes, further comprising a step of heating the semiconductor substratefor causing the refractory metal film and the second aluminum alloy filmto be alloyed, and also causing the refractory metal film to be alloyedwith the first conductive film layer in the bottom of the secondconnection holes.
 2. A method of fabricating a semiconductor devicecomprising:a step of forming a first interlayer dielectric film layer ina first region on a semiconductor substrate, a step of forming firstconnection holes for exposing the semiconductor substrate in the firstinterlayer dielectric film layer, a step of removing a first oxide filmfrom the exposed surface of the semiconductor substrate, a step offorming a first conductive film layer on the exposed surface of thesemiconductor substrate and on the first interlayer dielectric filmlayer, a step of forming a second interlayer dielectric film layer onthe first conductive film layer, a step of forming second connectionholes for exposing the first conductive film layer in the secondinterlayer dielectric film layer, a step of removing a native oxide filmfrom the exposed surface of the first conductive film layer, and a stepof forming a second conductive film layer on the exposed surface of thefirst conductive film layer and on the second interlayer dielectric filmlayer without exposing to air, wherein the first conductive film layercomprises a barrier metal film, an anti-reflection film and a firstaluminum alloy film, the second conductive film layer consists of arefractory metal film from 30 nm to 150 nm thick and a second aluminumalloy film formed on the refractory metal film, and forming of therefractory metal film and forming of the second aluminum alloy film aredone continuously without being exposed to atmosphere, wherein theanti-reflection film is formed on the first aluminum alloy film and thefirst aluminum alloy film is then exposed by the second connectionholes, and wherein the first conductive film layer is thinner inthickness than the second conductive film layer.
 3. A method offabricating a semiconductor device comprising:a step of forming a firstinterlayer dielectric film layer in a first region on a semiconductorsubstrate, a step of forming first connection holes for exposing thesemiconductor substrate in the first interlayer dielectric film layer, astep of removing a first oxide film from the exposed surface of thesemiconductor substrate, a step of forming a first conductive film layeron the exposed surface of the semiconductor substrate and on the firstinterlayer dielectric film layer, a step of forming a second interlayerdielectric film layer on the first conductive film layer, a step offorming second connection holes for exposing the first conductive filmlayer in the second interlayer dielectric film layer, a step of removinga native oxide film from the exposed surface of the first conductivefilm layer, and a step of forming a second conductive film layer on theexposed surface of the first conductive film layer and on the secondinterlayer dielectric film layer without exposing to air, wherein thefirst conductive film layer comprises a barrier metal film, ananti-reflection film and a first aluminum alloy film, the secondconductive film layer consists of a refractory metal film from 30 nm to150 nm thick and a second aluminum alloy film formed on the refractorymetal film, and forming of the refractory metal film and forming of thesecond aluminum alloy film are done continuously without being exposedto atmosphere, wherein the anti-reflection film is formed on the firstaluminum alloy film and the first aluminum alloy film is then exposed bythe second connection holes, and wherein each of the second connectionholes has a taper at the upper part and the upper opening size is largerthan the lower opening size.